Generally, a ceramic gas sensor is to detect particular gas. When the gas sensor is exposed on particular gas, a conductivity of ceramic as gas sensitive material is changed or an electromotive force thereof is generated so that it is possible to detect particular gas by measuring the conductivity or the electromotive force. In the ceramic gas sensor as above, to improve sensitivity and selectivity for particular gas, catalytic material is doped into the ceramic and further, the temperature should be kept higher than 300° C. Hence, power consumption of the ceramic gas sensor is higher than that of the other ones. Therefore, in order to enlarge the application range of the ceramic gas sensor, it is most important to provide the ceramic gas sensor with low power consumption but keeping the ceramic at high temperature.
Referring to FIG. 1, there is provided a cross sectional view of a conventional gas sensor 100 disclosed in U.S. Pat. No. 5,759,367 titled “GAS SENSOR”. The conventional gas sensor comprises an insulating glass film 4 formed on a silicon substrate, heater films 8, 10, made of gold (Au), which are formed on top of the insulating glass film 4, an insulating layer 14, detection electrodes 18, 20, formed on top of the insulating layer 14, and a gas sensitive film 16 surrounding the detection electrodes 18, 20. In this gas sensor 100, the heater film 6 heats up the gas sensitive film 16 and a variation of the gas sensitive film 16 is detected according to the change of the gas flown thereinto, by using the detection electrodes 18, 20.
The gas sensor 100 as aforementioned has a drawback that the gas sensitive film 16 is disposed on the detection electrodes 18, 20 so that the fabrication process becomes complicated. That is, each mask is needed for patterning the heater films 8, 10 and the detection electrodes 18, 20, respectively. Moreover, since the gas sensitive film 16 is formed on a top surface of the heater film 6 and a bottom portion of the heater film 6 is directly in contact with the insulating glass film 4, the heat loss into the silicon substrate becomes considerably raised.